From 65a4de0ffd975af7e2ffc9acb875b6a8ae7ee1aa Mon Sep 17 00:00:00 2001 From: Yan Zhao Date: Fri, 8 Mar 2024 17:09:28 -0800 Subject: [PATCH] KVM: x86: Ensure a full memory barrier is emitted in the VM-Exit path Ensure a full memory barrier is emitted in the VM-Exit path, as a full barrier is required on Intel CPUs to evict WC buffers. This will allow unconditionally honoring guest PAT on Intel CPUs that support self-snoop. As srcu_read_lock() is always called in the VM-Exit path and it internally has a smp_mb(), call smp_mb__after_srcu_read_lock() to avoid adding a second fence and make sure smp_mb() is called without dependency on implementation details of srcu_read_lock(). Cc: Paolo Bonzini Cc: Sean Christopherson Cc: Kevin Tian Signed-off-by: Yan Zhao [sean: massage changelog] Tested-by: Xiangfei Ma Tested-by: Yongwei Ma Link: https://lore.kernel.org/r/20240309010929.1403984-5-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 869cfaa980bd..121907049190 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11135,6 +11135,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) kvm_vcpu_srcu_read_lock(vcpu); + /* + * Call this to ensure WC buffers in guest are evicted after each VM + * Exit, so that the evicted WC writes can be snooped across all cpus + */ + smp_mb__after_srcu_read_lock(); + /* * Profile KVM exit RIPs: */ -- 2.25.1